Tone detector



Aug. 4, 1970 A. R. SALDUTTI ETAL TONE DETECTOR Filed Aug. 17, 1967 SMQ-I-I-I. ilmi. il Qwnlk SUQJ m wl. U Qwsk w @gua/AM ANOREW R. SALUTT/.STEVf/V A. 57`CKR AGENT United States Patent Office 3,522,544 TONEDETECTOR Andrew Rocco Saldutti, Clark, NJ., and Steven A.

Steckler, Brooklyn, N.Y., assignors to International Telephone andTelegraph Corporation, Nutley, NJ., a corporation of Maryland Filed Ang.17, 1967, Ser. No. 661,345 Int. Cl. H03k 9/06 U.S. Cl. 328-138 9 ClaimsABSTRACT OF THE DISCLOSURE -A Q multiplier increases the Q of a LCcircuit tuned to frequency F and provides a peaked output for an inputtone having a frequency F. The peaked output and the given input toneare subtracted from each other by a differential amplifier providing anull output. The peaked output and the null output are rectified andcombined producing an output. An input tone having a frequency otherthan F will produce an output from the differential ampliiier which willprevent the production of the output.

BACKGROUND OF THE INVENTION This invention relates to communicationsystems and more particularly to a tone detector for communicationsystems employing a tone having a single given frequency for conveyinginformation.

A tone having a single given frequency can be employed in many types ofcommunication systems to convey intelligence. For instance, the tone canbe keyed at a control center With an order to Operate apparatus at aremote point. In another system, the tone can be keyed in accordancevvith meter readings, or the like, to enable a control center to read ameter disposed at a point remote from the control center. In an orderWire system, a tone disposed in the voice band can be utilized foraddress purposes to prepare a remote terminal for receipt of voiceinformation.

In all such systems, it is necessary to provide a detector for the toneconveying the information which is nonresponsive to spurious tones and/or voice intelligence. In the past such detectors have employed twolarge, high Q tuned circuits.

SUMMARY OF THE INVENTION An object of this invention is to provide animproved tone detector for utilization in communication systems of thetype described above and the like.

Another object of this invention is to provide a tone detector employinga single, relatively low Q tuned circuit.

Still another object of this invention is to provide a tone detectoremploying components of reduced size.

A further object of this invention is to provide a tone detector thatmay be manufactured employing microelectronic techniques.

A feature of this invention is the provision of a detector for a tonehaving a given frequency comprising an input terminal, a tuned circuitcoupled to the input terminal, the tuned circuit being tuned to thegiven frequency and having a given value of Q, first means coupled tothe tuned circuit to increase the value of Q, and second means coupledto the input terminal and the first means to produce an output inresponse to an input tone having a given frequency and no output inresponse to input tones having frequencies other than the givenfrequency.

BRIEF DESCRIPTION OF THE DRAWINGS The above mentioned and other featuresand objects of this invention vvill become more apparent by reference tothe following description taken in conjunction with the 3,522,544Patented Aug. 4, 1970 DESCRIPTION OF THE PREFERRED EMBODIMENT Referringto the figure, the detector of this invention includes input terminal 1to which tuned circuit 2 is coupled, circuit 2 being tuned to thefrequency of the tone which is desired to be detected and having arelatively low value of Q. Q multiplier 3 coupled to tuned circuit 2increases the Q of the tuned circuit by a given factor, for instance, bya factor of 10. `One input of differential amplifier 4 is coupled toterminal 1 and the other input of differential amplifier 4 is coupled topoint B, the output of Q multiplier 3. The output of Q multiplier '3,point B, is coupled to voltage doubler rectier 5 and the output ofdifferential amplifier 4, point A, is coupled to a second voltagedoubler rectifier 6. The outputs of the voltage doubler rectifiers 5 and6 are combined to produce a control voltage (BDC-ADC) 'which is used tocontrol the conduction of relay driver 7 through the means of thecircuitry including transistor Q5.

More specifically, tuned circuit 2 includes inductance Ll and capacitorsC1 and C2. Tuned circuit 2 is coupled to terminal 1 by resistor R1. TheQ multiplier includes transistor Q1 having its base coupled to resistorR1 With its emitter electrode coupled to the base electrode oftransistor Q2. The collectors of transistors Q1 and Q2 are coupled to apositive voltage -}V1 by resistor R3. The emitter of transistor Q2 iscoupled to the junction of capacitors C1 and C2 by resistor R2 and alsoby load resistor R4 to a negative voltage -V2.

Differential amplifier 4 includes transistors Q3 and Q4 and theirassociated interconnecting resistors R6, R7, R9, R10, R12, R13 and R14.Resistor R8 provides one input for the differential amplifier and iscoupled between terminal 1 and the base of transistor Q3. Resistor R5constitutes the other input for differential amplifier 4 and is coupledbetween point B and the base of transistor Q4. Resistor R11 constitutesthe load resistor for the differential amplifier 4 and provides anoutput therefrom at point A. Point A is coupled to voltage doublerrectifier 6 which includes the coupling capacitor C3, diodes CR1 andCRZ, capacitor C4 and load resistor R15. The output of Q multiplier 3,point B, is coupled to Voltage doubler rectifier S ywhich includes thecoupling capacitor C5, diodes CRS and CR4, capacitor C6 and loadresistor R16. The rectifier 5 has its load resistor R16 coupled toground and interconnected to R15 of rectifier 6i by conductor 8 toprovide the control voltage (BDC-ADC) at the base of transistor Q5. Thecollector of transistor Q5 is coupled t0 the positive -j-Vl voltage byresistor R17 and the emitter of transistor Q5 is coupled to the negativesupply voltage -VZ by resistor R18. The emitter of transistor Q5 iscoupled to the base of transistor Q6, a part of relay driver 7, by meansof diodes CR6 and CR7. The base of transistor Q6 is coupled to the -l-Vlvoltage by resistor R19 and the emitter of transistor Q6 is coupled toground by resistor R20. The collector of transistor Q6 is coupled to-I-Vl by diode CRS vvhile the collector is directly coupled to a relay(not sho-Wn) along with the -i-Vl supply voltage.

The operation of the detector in accordance with this invention is toprovide an output indication when a tone is present having a frequencyequal to the frequency at which tuned circuit 2 is tuned, in otherwords, at a frequency When the tone of the given frequency is present, Qmultiplier 3 provides a peak output across resistor R4 at point B. Also,the output of the differential amplifier 4 provides a null output acrossresistor R11 at point A when the given tone is present. After beingrectified in rectifiers 5 and 6 there is a control voltage ofsubstantially -i-BDC at the base of transistor Q5 which Will render thistransistor and transistor Q6 of relay driver 7 conductive to operate therelay and give an indication of the receipt of the tone and enabledetection of the information contained thereon. When any other signalhaving a frequency different than F is applied to terminal 1 there willbe substantially no output across resistor R4 at point B and there willbe a substantial negative output across resistor R11?` at point Aresulting in a -ADC control voltage on the base of transistor Q5 whichwill drive this transistor into cut off and render transistor Q6 ofrelay drive 7 nonconductive and, thus, the relay inoperative.

Therefore, in the arrangement of the tone detector of this invention thedetector will respond to a tone having a frequency F but will benonresponsive to signals (voice frequencies) or tones of any otherfrequency.

Due to the size and type of components employed in the tone detector ofthis invention this tone detector lends itself to manufacturing byutilizing microelectronic techniques and, therefore, will provide arelatively small modular unit to be employed in communication systemswherein a tone of a single given frequency is employed for conveyingintelligence.

While we have described above the principles of our invention inconnection with specific apparatus, it is to he clearly understood thatthis description is made only by way of example and not as a limitationto the scope of my invention as set forth in the objects thereof and inthe accompanying claims.

We claim:

1. A detector for a tone having a given frequency comprising:

an input terminal;

a tuned circuit coupled to said input terminal, said tuned circuit beingtuned to said given frequency and having a given value of Q;

first means coupled to said tuned circuit to increase said value of Q;

differential amplifier means coupled to said input terminal and saidfirst means to subtract the output signal of said first means and theinput tone; and

second means coupled to said differential amplifier means and said firstmeans to produce a finite output signal in response to an input tonehaving said given frequency and no output signal in response t0 inputtones having frequencies other than said given frequency.

2. A detector according to claim 4, wherein said tuned circuit is an LCtuned circuit having a relatively low value of Q.

3. A detector according to claim 4, wherein said first means includes aQ multiplier.

4. A detector for a tone having a given frequency comprising:

an input terminal;

a tuned circuit coupled to said input terminal, said tuned circuit beingtuned to said given frequency and having a given value of Q;

first means coupled to said tuned circuit to increase said value of Q;and

second means coupled to said input terminal and said first means toproduce an output in response to an input tone having said givenfrequency and no output in response to input tones having frequenciesother than said given frequency;

said second means including;

third means coupled to said input terminal and Cil said first means tosubtract the output of said first means and the input tone,

a first rectifier means coupled to said first means,

, a second rectifier means coupled to said third means, a fourth meanscoupled to said first and second rectifier means to combine therectified outputs therefrom to produce a control signal, output meansfor said detector, and fifth means coupled between said fourth means andsaid output means responsive to said control signal to control and theproduction of an output from said output means. 5. A detector accordingto claim 4, wherein said third means includes:

a differential amplifier.

6. A detector according to claim 4, wherein each of said first andsecond rectifier means include:

a voltage doubler rectifier.

7. A detector according to claim 4, wherein said output means includes:

a relay driver whose conduction is controlled by said fifth means.

8. A detector for a tone having a given frequency comprising:

an input terminal;

a tuned circuit coupled to said input terminal, said tuned circuit beingtuned to said given frequency and having a given value of Q;

first means coupled to said tuned circuit to increase said value of Q;and

second means coupled to said input terminal and said first means toproduce an output in response to an input tone having said givenfrequency and no output in response to input tones having frequenciesother than said given frequency;

said tuned circuit being an LC tuned circuit having a relatively lowvalue of Q;

said first means including:

a Q multiplier; and said second means including:

third means coupled to said input terminal and said Q multiplier tosubtract the output of said Q multiplier and the input tone,

a first rectifier means coupled to said Q multiplier,

a second rectifier means coupled to said third means,

fourth means coupled to said rst and second rectifier means to combinethe rectifier outputs therefrom to produce a control signal,

output means for said detector, and

fifth means coupled between said fourth means and said output meansresponsive to said control signal to control the production of an outputfrom said output means.

9. A detector according to claim 8, wherein said third means includes:

a differential amplifier; each. of said first and second rectifier meansinclude:

a voltage doubler rectifier; and

said output means includes:

a relay driver Whose conduction is controlled by said fifth means.

References Cited UNITED STATES PATENTS 2,920,280 1/1960 Pentecost328-138 X 2,951,973 9/1960 Atkinson 328-138 X 3,173,065 3/1965 Fullerton307-233 X 3,223,929 12/1965 Hofstad et al 307-233 X JOHN S. HEYMAN,Primary Examiner U.S. Cl. X.R.

